Friction welding



WW M. HOLLANDER ETAL p fi FRICTION WELDING Original Filed Aug. 12, 19593 Sheets-Sheet 1 INVENTORSI MILTON B. HOLLANIDER EDGBAYR L. VANROSENBERG FRICTION WELDING .3 Sheets-Sheet 2 Original Filed Aug. 12,1959 FIG. 6

INVENTORSI B. HOLLANDER EDgR L. VON ROSENBERG FIG. BOB

MILTON Aug.

av 39% M. w. HCDLLAMDER ETAL 3,25%,M93

FRICTION WELDING Original Filed Aug. 12, 1959 v 3 $heets-$heet 5INVENTORSZ HOLLAND'ER I... VAN ROSENBERE United States Patent 3,269,003FRIQTIUN WELDING Milton Bernard Hollander, Teaneck, N.J., and Edgar LynnVon Rosenberg, Oklahoma City, Okla, assignors to American Machine &Foundry Company, a corporation of New Jersey Original application Aug.12, 1959, Ser. No. 833,339, now Patent No. 3,134,278, dated May 12,1964. Divided and this application May 1, 1964, Ser. No. 377,436

2 Claims. (Cl. 29--470.3)

This application is a division of our copending application Serial No.833,339, filed August 12, 1959, now Patent No. 3,134,278, issued May 12,1964.

This invention relates to methods and apparatus for welding metalworkpieces using heat generated by friction as the pieces to be weldedare rubbed against each other. More particularly, this invention relatesto the friction welding of metal workpieces by rotating one workpiecerelative to the other while the workpieces are pressed together untilsufficient heat is generated to effect a weld and thereafter stoppingthe relative rotation While the workpieces are continued to be pressedtogether until the weld is completed.

Conventional welding practice requires a separate source of heat toreduce the portions of the workpieces to be joined to a molten orplastic state. Sometimes additional filler metal is added to bond thewelded pieces together or brazing is employed. The separate source ofheat is commonly provided by an oxyacetylene flame, high frequencyinduction, an electric current passed through the pieces as inresistance welding, or by an electric arc. Although conventional methodsproduce firm welds for certain uses, this invention provides a superiorweld for many specific applications.

Another form of metal working involves spinning a tool against a metalto be formed to generate heat either in the workpiece or in an adjacentsolder material. The tool is then reused and does not fuse to theworkpiece. Solder or welding stock may also be rotated to produce enoughheat to flow the stock material into a joint between workpieces. In noneof these methods is a metal workpiece rubbed against a piece to which itis to be fused.

Although spin welding is known in the art of working thermoplasticpolymer resins, the treatment of metals presents complex problems whichare not analagous to thermoplastic resins.

In brief summary, the invention relates to a method of friction weldingwhich comprises the steps of:

(a) Rotating metal workpieces relative to each other;

(b) Rubbing said workpieces together under pressure, either at aconstant speed or at a declining speed, to bring said workpieces towelding condition after which torque between the workpieces changesabruptly;

(c) Detecting the change of torque;

(d) Rapidly bringing rotation to a stop in response to the change oftorque and continuously forcing the workpieces together.

An object of this invention is to provide a method for welding metalworkpieces having weld areas which may be developed by revolution.

Another object of this invention is to provide a method for more easily,cheaply, efiiciently, securely and cleanly butt welding cylindrical ortubular metal workpieces.

Yet another object of this invention is to provide a means to welddissimilar metals or alloys that are difficult or impossible to weldconventionally.

Still another object of this invention is to provide a method of weldingmetal workpieces by the generation of the smallest amount of heat in theshortest possible period of time to prevent excessive decarburization,de-

3,269,063 Patented August 30, 1966 ice formation of the workpieces, orlike undesirable effects in the area of the weld.

A further object of this invention is to provide a welding device whichhas a lower power requirement. The low power requirement is inherent inthe friction welding process. Also, the maximum power demand can bereduced by storing rotational energy in a flywheel over a period of timeuntil it is needed for the relatively short welding cycle.

A still further object of this invention is. to provide a frictionwelding device which has a welding cycle controlled by any of thefollowing means, singly or in combination: thermoelectric or infra-redsignals from the area of the weld; the relative movement towards eachother of the workpieces after initial contact; or the torque exertedbetween the workpieces during the generation of heat and the formationof the weld.

Yet a further object of this invention is to provide interlocking tapersand/or teeth at the ends of workpieces to be friction welded so thatchatter is reduced, the weld strength and zone area is increased andproper alignment is assured. The increase in weld zone area therebyobtained provides stronger joints even with less efiicient welds.

An additional object of this invention is. to provide a machine, for thefriction butt welding of workpieces, which rotates the workpiecesrelative to each other, forces the workpieces together while rotating,holds them firmly to prevent any vibration or chatter, rapidly stops therelative rotation of the workpieces to complete the weld, applies asecond higher pressure to squeeze excess melted metal from the Weldzone, serves as a lathe to trim the ends of the workpieces to the propershape and alignment before they are welded, and serves as a lathe toturn off excess upset metal after the weld is completed.

Another additional object of this invention is to provide a superiormethod to weld bands to generally cylindrical objects such as therotating bands which are Welded to military projectiles.

A further additional object of this invention is to provide a lighter,more rugged, and simpler welding apparatus which may be mounted on avehicle to weld tool joints and similar couplings to oil well drill pipein the field.

Still other objects, advantages, and features of invention which residein the construction, arrangement and combination of parts involved inthe invention and its practice will be understood from the followingdescription and accompanying drawing wherein corresponding elements aredesignated by similar characters and in which:

FIG. 1 is a side view, partly broken away in section, of an apparatusfor friction welding;

FIG. 2 is a section taken on line 2-2 of FIG. 1;

FIG. 3 is a side view, partly broken away in section, of the frictionwelding apparatus modified and adapted for welding tool joints to drillpipe;

FIG. 4, FIG. 5 and FIG. 6 are longitudinal sections through a length ofdrill pipe with tool joints shown in position before welding, afterwelding, and after the upset is machined off;

FIG. 7 shows a cover providing a controlled atmosphere in the area of aweld;

P16. 8 shows a third intermediate piece positioned between twoworkpieces to be friction welded;

FIG. 9 is a longitudinal section showing the third intermediate piecebonding the two workpieces after friction welding;

FIG. 10A shows a cylindrical workpiece in position to be friction weldedto a non-cylindrical workpiece shown in section;

FIG. B is a perspective view showing the cylindrical workpiece of FIG.10A friction welded to the non-cylindrical workpiece;

FIG. 11A.is a longitudinally cross sectional view of two workpieces oftubing positioned for friction welding and showing multiple interlockingsaw tooth ridges on the abutting surfaces thereof;

FIG. 11B is an end view of one of the workpieces of FIG. 11A;

FIG. 12 is a side view of a conventional round of ammunition orprojectile with the casing and the windshield shown in section;

FIG. 13 is a side view of a projectile similar to that shown in FIG. 12,but slightly modified so as to have both a rotating band and awindshield, friction welded to it with the rotating band and thewindshield shown in longitudinal section in position to be welded;

FIG. 14 is a side view of the projectile shown in FIG. 13 with therotating band and the windshield shown in longitudinal section frictionwelded to it;

FIG. 15 is a side view of a fragment of a front portion of anotherprojectile with a specially modified windshield shown in longitudinalsection in position to be friction welded to it;

FIG. 16 is a side view of the fragment of the front portion of theprojectile shown in FIG. 15 with the modified windshield shown inlongitudinal section friction welded to it;

FIG. 17 is a front view of a split clamp holding a split ring rotatinghand against a projectile shown in section for friction welding; and

FIG. 18 is a longitudinal section through the split ring rotating bandof FIG. 17 especially adapted for friction welding.

Referring to the drawing in detail, FIGS. 1 and 2 show a 'basic frictionwelding apparatus as a preferred form of the invention. On the base 20there are fixed a first vertical frame member 21 and a second verticalframe member 22. These are connected top and bottom by heavy horizontalframe members 23 and 24. The horizontal frame members 23 and 24 areshown as heavy rods secured by nuts 25. However, any suitable framestructure which is preferably rectangular could be used. Within thesecond vertical frame member 22 there is fixed a workpiece holding chuck26 by a suitable self-aligning support mechanism 27. Extending throughthe first vertical frame member 21 is the spindle 28 with a workpieceholding chuck 29 fixed to its innermost end to rotate with. it. Ahydraulic cylinder 30 has a heavy plunger 31 working within it. Thisplunger 31 is supported at its inwardly disposed end by a yoke 32 whichis slidably secured by the horizontal frame members 23 and 24. Since thespindle 28 is rotatably journaled within the plunger 31, the yoke 32gives maximum support to the chuck 29 to prevent any unwanted vibrationas it is rotated. A set of pulleys 33 and 34, mounted respectively onthe spindle 28 and on a drive shaft 36, are connected by suitablebelting 37 or by other transmission means. A high speed motor 38 drivesthe shaft 36 through a clutch 39. A brake 40 is mounted on the driveshaft 36 to stop rapidly both it and the spindle 28 which carries thechuck 29.

In the operation of this apparatus workpieces 41 and 42 are securedrespectively in the stationary chuck 26 and the driven chuck 29. If theworkpieces to be welded have square ends, the stationary chuck 26 wouldnot be self-aligning, but it would be rigidly fixed to the secondvertical frame member 22. If the workpieces have suitable end forms, aswill be later described, the chuck 26 may be self-aligning, as shown.The clutch 39 is engaged and the workpiece 41 is rapidly rotated.Hydraulic fluid is forced into the cylinder 30 to move the plunger 31outward and bring the workpieces together. Heavy duty thrust bearings 43take the load from the chuck 29. As soon as the proper conditions arereached at the contact surface between the workpiece, the clutch 39 isdisengaged and the brake 40 is applied. In a test machine, a magneticclutch 39 was used with an electric brake 40 as these were easilycontrolled to provide an automatic Welding cycle.

To weld two pieces of metal according to this invention, severalconditions are of great importance. The surfaces to be welded should beaccurately aligned before and during the welding process to maintainuniform contact pressure over the entire area to be Welded. Theworkpieces should be rigidly held in position so that they cannotvibrate or chatter during the welding. The relative sliding speed at theweld surface should be at least 50 feet per second for most steels. Theangular velocity then depends on the size of the workpieces and thecharacteristics of the metal being welded. For example, a one-inchdiameter AISI 4140 steel workpiece requires a rotational speed of about5,000 r.p.m. The contact pressure at the weld area should be betweenabout 1,000 to 10,000 p.s.i. depending on the size and character of themetal being welded and the dimensions of the section. A one inch AISI4140 steel workpiece requires about 3000 p.s.i. contact pressure. Underthese conditions, a thin molten film about 0.005 inch thick is formed atthe area of contact. This is sutficient to fuse the metal and form aweld bonding the workpieces. Rotation must be stopped after the moltenfilm has formed and the upset or plastic fiow of metal has reached aprescribed amount. If this rotation is not stopped within a time whichdepends on the material being welded and the shape of the weld surface,the weld will be broken. The apparatus, which has been described, meetsthese requirements and produces firm welds.

FIG. 3 shows a modification of the basic friction welder of FIG. 1 whichis set up to weld tool joints or couplings on drill pipe or collars andis another example of the invention. Inplace of a stationary chuck fixedto frame member 22, a rotary chuck 45 is fixed to a hollow shaft 46which may accommodate a length of drill pipe 47 'within it. The drillpipe 47 is gripped by the chuck 45 and may be rotated by a first motor48 which drives the first shaft 46 by means of pulleys 49 and 50 and abelt 51. A suitable first clutch 52 divides the first shaft 46 whichalso has a first brake 53 fixed to it. On ways 54, which may be similarto those of a lathe bed and which may be built to swing into and out ofposition, there is mounted a tool holder 55 on the saddle 56. A lowspeed second motor 57 may drive the spindle 58 through the pulleys 59and 60 andthe second clutch 61. A high speed third motor 62 may turn thesecond shaft 63 through the pulleys 64 and 65 which step up the speed ofthe second shaft 63 from that of the third motor 62. A fiywheel 66 ofconsiderable mass is mounted on the second shaft 63. A third clutch 67allows the second shaft 63 to drive the speed reducing pulleys 68 and 69so that the spindle 58 turns at a lower rate of speed than the flywheel66. A second brake 70 is mounted on the second shaft 63 beyond thepulley 68 to stop the spindle 58.

In the operation of this embodiment of the invention a piece of drillpipe 47 which is also equivalent to a drill collar is fixed in the chuck45 within the first shaft 46. The length of the drill pipe 47, whichextends far beyond the shaft 46, may be held for rotation by enoughsupports 71 to prevent the drill pipe 47 from whipping as it turns. Atool joint 72 is placed in the chuck 29. If the clutches 52 and 61 areengaged, the first and second motors 48 and 57 can rotate the tool joint72 and the drill pipe 47 at a slower speed, for example about r.p.m.This allows the tool holder 55 to be run in with the hand wheel 73 toface off both the drill pipe 47 and the tool joint 72. This ensuresmatching and alignment of these turned off faces when they arethereafter brought together for friction welding.

If the first and second clutches 52 and 61 are then disengaged, thedrill pipe 47 may be held static and locked with the brake 5-3. If thethird motor 62 is allowed to run for a short time, it can storeconsiderable energy in the flywheel 66. Through the third clutch 67,this motor will also rapidly rotate the spindle 58. By activating thehydraulic cylinder 30, the rapidly rotating tool joint 72 is forcedagainst the stationary drill pipe 47 with the thrust bearings 43 and 47taking up the force. When the proper conditions have been reached, theweld can be completed as the third clutch 67 is disengaged and thesecond brake 70 is applied to stop the relative rotation of the tooljoint and the drill pipe. Higher pressure must be applied and maintainedby the hydraulic cylinder 30 to force excess melted metal out of theweld zone just after the brake is applied.

It has been found that the actual power required while making such aweld will be about horsepower per square inch of weld surface. Sincethis power is only needed for or seconds, and several minutes may berequired between welds to chuck up new workpieces, a lower horsepowerthird motor 62 may be used if it stores energy for the period of deadtime in a flywheel. If a 200 HJP. motor would be needed to weld a 20square inch joint on a drill pipe, a suitable flywheel can easily reducethis power requirement to a H.P. motor with the great resulting savingin motor weight. This is an important consideration in a mobile unit foruse in the field. During the actual weld cycle, the maximum speed of theflywheel and the spindle can fall off up to 20 percent as the weldingtakes energy from the flywheel, but the initial speed must be highenough to allow for this reduction. Although a smaller flywheel may beused to store the required amount of energy if it is turned faster thanthe spindle as shown in FIG. 3, a larger flywheel could be mounteddirectly on the spindle on non-mobile machines.

As shown in FIG. 4, the tool joints 72 and 72' and the correspondingends of the drill pipe 47 may be prepared with the matching tapers 75and 76 by turning them in the welding apparatus in the manner that hasbeen described. These tapers have been found to reduce chatter andvibration during the actual welding operation. They also provide agreater welding surface and a stronger weld. This feature of theinvention is illustrated in FIG. 11A and FIG. 11B. As the weld iscompleted as shown in FIG. 5, a certain amount of metal 77 and 78 upsetsor flows plastioly. This upset may appear to be different in size andshape from that shown in the drawing. The chuck 29 may then bedisengaged and withdrawn and the tool holder may be used with suitablecutting tools, boring bars or grinding devices to remove the upset metal77 and 78 as the welded drill pipe and tool joint are turned by thefirst motor 48. Thus this apparatus makes possible a smooth weld asshown in FIG. 6. Furthermore, such a weld can now be made using a mobilefriction welding unit in the field where the drill strings areassembled.

This invention provide many advantages because the heat forming the weldis generated at the point of contact of the workpieces where it isneeded and there is no unnecessary heat generated. If the weld cycle israpid enough, energy is converted to heat only as it is needed toperform the actual weld. This prevents overheating of the workpieces andexcessive decarburization and upset. Also slight impurities which may bepresent in the weld will tend to flow out of the weld zone with theupset while no foreign matter, such as fluxes or bonding materials, needbe added. Although the drill pipe 47 has been shown stationary duringthe welding process, it could be counter-rotated by means of the firstmotor 48 to increase the relative rotational velocities of the pieces tobe welded. In certain applications, counter-rotating pieces, each drivenat a high speed and having its own fast braking system, allow a muchfaster weld cycle with the 6 obvious resulting advantages. Also, smalldiameter sections of about one inch or less may require excessively highrotational speeds to attain the required surface velocities unlesscounter-rotation is used.

Although the butt welding of tubular workpieces has been described,solid cylindrical workpieces may be just as easily butt welded as thehigher relative velocity of the edges of the workpieces generates heatfaster and renders the outer edges plastic before the center is heated.This allows the edges to flow under pressure and to concentrate theforce urging the workpieces together at the cooler, unmelted center.This concentration of pressure, along with heat soaking in from theperiphery, soon renders the center molten enough for welding. Forexample, rivets or similar fastening means can be welded in place.

As shown in FIG. 7, the chucks 26 and 29 may be enclosed in acylindrical casing 80 into which a controlled atmosphere may beintroduced through a tube 81. Certain metals, such as magnesium andzirconium, should be friction welded in an inert atmosphere to preventoxidation and because of the safety hazard of explosion or fire. Inother applications, special atmospheres at high pressures may benecessary to prevent or combat excessive decarburization. A preheating,carburizing gas flame may also be used as may induction coils to heattreat a completed weld and prevent a too rapid air quench which is theusual means of cooling and completing the weld.

One great advantage of the friction welding of metals is that dissimilarmetals may be joined in a firm weld. Brass and copper can be weldeddirectly to steel and aluminum can be directly welded to brass or steel.Limitations seem to appear in the welding of dissimilar metals whenthere is an extreme difference in their melting points, heatconductivities and solubilities of the lower melting alloy into thehigher melting alloy. FIG. 8 shows how even this difliculty can beovercome. If the workpieces 82 and 83 are rotated in the same ordifferent directions and a thin wafer of material 84 is held stationaryand placed between them as they are brought together, a weld such asthat shown in FIG. 9 would result. If the workpiece 82 of a lowermelting point or heat conductivity were to be welded to a workpiece 83of a higher melting point or heat conductivity, a wafer 84 withintermediate properties could be used to ensure a firm weld.

FIGS. 10A and 10B show that friction welding is not confined to the buttwelding of two cylindrical pieces. A stud 85 is shown welded to a plate86.

FIG. 11A and FIG. llB show the edges of the workpieces 85 tapered to fitinto a socket or interlocking taper in the second workpiece $6. Thistaper can include a number of concentric ridges and correspondingdepressions on weld surfaces. In profile this would appear as a sawtooth arrangement. Pieces lock together in alignment and a stronger weldresults from the larger welded area of multiple interlocking tapers.

In another embodiment of the invention FIG. 12 shows a conventionalround of ammunition in which a projectile is seated in a casing 91containing an explosive propelling charge 92. The projectile 90 ismachined from solid or hollow blanks of steel and a softer rotating band93 of low carbon steel or brass is swaged onto the projectile. Thesofter rotating band is cut by the rifling and forms a relatively gastight seal to confine the propelling gases as it grips the rifling whichimparts rotation to the projectile as it travels down the bore.

The conventional swaging operation to secure the rotating band 93 to theprojectile 90 requires that the projectile be especially knurled ormachined to accept the band. These operations take time and areexpensive. If the band is welded in place using conventional weldingtechniques, the high temperature of the weld puddle can either collapseor deform thin walled projectiles or necessitate subsequent heattreatment to relieve residual stresses. The rough, irregular appearanceof conventional welds also requires a final machining of the weld area.

This invention includes making a taper 94 on the projectile as shown inFIG. 13 and forming a special rotating band 95 which has a correspondinginner taper 96. Then the projectile 90 and the rotating band can berotated relative to each other, as has been described, to give arelative surface speed in excess of 50 feet per second (for example, forAISI 4140 steel). When the band is held against the projectile withsufficient force so that a pressure of over 2000 p.s.i. results in thecontact area, a friction weld may be made. The friction welding cyclemay be so brief that the upset is small and uniform and requires nofurther machining. The heat may be so localized and generated for such abrief period of time that the projectile does not deform and nosubsequent heat treating is needed. The relative rotation of the partsto be welded in this application of friction welding may be stopped bymerely releasing the band 95. FIG. 14 shows the band 95 welded to theprojectile in this manner.

FIG. 17 shows an alternate procedure whereby a special circular splitclamp 97 may be used to compress a split ring rotating band 98 to applya normal force between the rotating projectile 90 and the band 98 andthereby eliminate the need to use the tapered geometry. FIG. 18 shows arotating band 93 modified with an offset split 87 so that it can bewelded to a projectile. This method for attaching rotating bandsrequires no special preparation or modification of the projectiles.

The thin conical windshield 99 shown in FIG' 12 is used to stabilize theprojectile 90 during its flight. In current practice this windshield 99is resistance welded or glued to the projectile 90, but neither methodhas proved entirely satisfactory or reliable.

As shown in FIG. 13, this invention contemplates rotating the projectile90 while the windshield 99 is held against it to be friction welded inplace as shown in FIG. 14. As the metal at the interface of thewindshield 99 and projectile 90 becomes molten and deforms during thewelding, it may flow to result in the thinner, weaker portion 88. Inthose cases where this is found to be troublesome, a thicker innerportion 89, as shown in FIG. 15, may be provided in the weld zone sothat, after the deformation of the windshield in welding, its thicknessat the weld is as great or greater than the surrounding wall thickness.FIG. 16 shows such a windshield welded in place with the weld area ofgreater thickness than the wall. In the friction welding of thin walledworkpieces such as these Windshields, special nesting fixtures may beneeded to surround the weld area so that sufiicient pressure can beexerted to complete the weld.

Friction welding particularly lends itself to the techniques ofautomation as many standard instruments can be used to register andcontrol the stages of the welding cycle. Referring to FIG. 1, a simplelimit switch 44 can be set to respond to the amount of the upset afterthe workpieces are first brought into contact with each other. Theswitch 44 reacts to motion of the spindle yoke 32 to disengage theclutch 39, apply the brake 40 and actuate a hydraulic servo valve toincrease the pressure of the cylinder 30 to complete the weld. This ispossible because the amount of the upset varies according to thedistance the workpieces are forced together. In a like manner,thermoelectric or infra-red signals generated by heat at the weld zonemay be used to control the weld cycle. The amount of torque registeredat the stationary chuck 26 by torque dynamometers may also be used withmost metals to control the weld cycle since the coefficient of frictionvaries as the metal in the weld zone reaches its melting temperature.

What is claimed is: 1. A method of friction welding comprising the stepsof (a) rotating metal workpieces relative to each other; (b) rubbingsaid workpieces together under pressure and at constant speed to bringsaid workpieces to welding conditions at which torque between theWorkpieces declines abnlptly; (c) detecting the change of torque; and(d) rapidly stopping rotation in response to said change of torque whilecontinuing to press the workpieces together. 2. A method of frictionwelding comprising the step of (a) rotating metal workpieces relative toeach other; (b) rubbing said workpieces together under pressure and at adeclining speed to bring said workpieces to welding conditions afterwhich torque between the workpieces abruptly increases; (c) detectingthe change of torque; and (d) rapidly stopping rotation in response tosaid change of torque while continuing to press the workpieces together.

References Cited by the Examiner UNITED STATES PATENTS 4/1924 Elverson73-9 9/1962 Jewett 7359 X OTHER REFERENCES JOHN F. CAMPBELL, PrimaryExaminer.

1. A METHOD OF FRICTION WELDING COMPRISING THE STEPS OF: (A) ROTATINGMETAL WORKPIECES RELATIVE TO EACH OTHER; (B) RUBBING SAID WORKPIECESTOGETHER UNDER PRESSURE AND AT CONSTANT SPEED TO BRING SAID WORKPIECESTO WELDING CONDITIONS AT WHICH TORQUE BETWEEN THE WORKPIECES DECLINESABRUPTLY; (C) DETECTING THE CHANGE OF TORQUE; AND (D) RAPIDLY STOPPINGROTATION IN RESPONSE TO SAID CHANGE OF TORQUE WHILE CONTINUING TO PRESSTHE WORKPIECES TOGETHER.